Exemplary embodiments of the present invention relate to an image encoding method, and more particularly, to an image encoding method using an adaptive preprocessing scheme, which compares an original image with the blocks of a reference image, encodes an image by replicating blocks having similarity within a threshold, and controls the threshold so that the picture quality of the encoded image remains within a specific range.
In order to transfer digital video from a source (e.g., a camera or stored video) to a destination (e.g., a player), core processes called compression (encoding) and restoration (decoding) are necessary. Through the processes, ‘original’ digital video that becomes a load of a bandwidth is compressed into a size that is easy to handle for transmission or storage and then restored again for display.
For the compression and restoration processes, the international standard ISO/IEC 13818, also known as MPEG-2, has been established for the digital video industries, such as digital TV broadcasting and DVD-video, and two compression standards: MPEG-4 Visual and H.264 have been developed in anticipation of the demands for an excellent compression tool. The H.264 standard, that is, a video compression technology standard established by ITU-T, is also called Moving Picture Experts Group-Phase 4 Advanced Video Coding (MPEG-4 AVC). The two compression standards have been subjected to the same creation process, and they have some common characteristics, but have different targets.
In general, an image encoding apparatus has been developed very effectively as the temporal or spatial entropy of an image to be encoded is reduced. The image encoding apparatus utilizes an image preprocessing scheme for processing an image so that better encoding is possible.
In an image preprocessing scheme for reducing the entropy of an image sequence, filtering and noise detection are used in order to remove pieces of noise distributed within an image. Representative examples for removing noise include a radiation correction scheme for reducing a radiation error occurring because the pixel value of an image is different from the radiation value of a real image and a geometric correction scheme for correcting the spatial distortion of an image having a twisted form.
In image compression, an object of image preprocessing is to reduce the amount of data of an image through a mathematical operation in order to increase efficiency and reduce a storage space when images are transmitted and received. Accordingly, in image compression intra-mode, a linear or non-linear filter for reducing or even removing high frequency components that account for most of image encoding costs is used.
A conventional technique, such as filtering for reducing the high frequency components, is problematic in that distortion is generated in an original image because a filter is used and thus a residual image is increased in an image compression process, thereby deteriorating compression efficiency.
A background technology of the present invention is disclosed in Korean Patent Laid-Open Publication No. 10-2011-0014507 (Feb. 11, 2011).